The present invention relates to a power monitoring system and, in particular, to an improved sensor for a power monitoring system.
Referring to FIG. 1, many electrical power distribution systems include a electrical panel enclosure 10 into which electric power is routed using one or more sets of wires 12. The electric power may have any voltage, any current, and any number of phases (e.g., single phase, two phases, or three phases). Each phase of the electric power is normally provided to a separate bus bar 14a, 14b, 14c which is normally an elongate conductor within the electrical panel enclosure 10. A plurality of circuit breakers 16a, 16b, 16c, etc. and branch circuit wiring electrically interconnect one or more of the bus bars 14a, 14b, and 14c to respective loads 18 that are typically located external to the panel enclosure 10. The circuit breakers 16 which are electrically connected to the bus bars 14a, 14b, 14c are commonly arranged in one or more vertically aligned rows 20 and 22 within the panel enclosure 10. Branch circuit wiring connects the circuit breaker 16 to the load 18 which commonly comprises a group of electrical loads, such as motors, lighting, heating units, cooling units, machinery, etc. The load may utilize single phase or multi-phase power. In the case of a three-phase load 18b, three wires will be used to connect a load to one or more circuit breakers. When the load 18 connected to a circuit breaker 16, shorts or otherwise draws excessive current, the circuit breaker 16 trips or otherwise disconnects the power to the load 18 to protect the wiring and the facility.
The total power usage by a facility may be readily obtained by reading the power meter provided by the power utility. The power meter is normally electrically interconnected between the electrical panel and the utility's distribution transformer. However, in many circumstances, it is desirable to monitor the power consumption of individual loads or groups of loads within a facility. Monitoring the power in a branch circuit permits effective sub-metering of different loads, buildings, or groups of loads to attribute the power usage to consumers obtaining power through the electrical distribution system. For example, power sub-metering may be used to attribute the power costs charged by the utility to different buildings, departments, or cost centers.
The traditional approach to monitoring such power usage is to install a power meter at a location proximate the load itself. To install a typical power meter on a three phase load, a current sensor is installed around each of the three wires that are connected to the load and a voltage connection is electrically interconnected to each wire. Such a power meter is available from Veris Industries, LLC under the name H8035 Power Meter. Unfortunately, it is burdensome to interconnect a significant number of power meters and in particular to make the voltage connections to the wires, especially if interconnections to the wires are not readily available. In addition, it is burdensome to interconnect the output of the power meters, if any, to a computer network because of the need to provide communication wiring or a wireless communication channel to each of the remotely located power meters. Also, installing the power meters requires significant expense for the technician to find a suitable location for the meter near each device to be monitored, in addition to the further expense of servicing the installed power meters.
Bowman et al., United States Patent Application Publication, Pub. No.: US 2003/0184280, incorporated herein by reference, disclose a branch circuit power monitoring system that can be mounted in or convenient to an electrical panel enclosure. The power monitoring system comprises a plurality of sensors connected to a power monitor that measures the voltage and phase angle at the bus bars in the electrical panel and the current in the various branch circuit wires connected to the circuit breakers. Power consumed by the load(s) attached to a branch circuit is calculated by the power monitor from the product of the current, the power factor, and the voltage.
The typical current sensor comprises a toroidal core having wire wound around the cross-section of the core over an arc of the torus. The branch circuit wiring connecting a circuit breaker to its respective load is routed through the aperture in the toroidal core of the current sensor. A varying current in the wire induces a current in the wire winding of the sensor that may be used directly or converted to a signal, for example, a voltage signal, from which the power monitor can determine the magnitude of the current flowing in the wire passing through the aperture in the sensor.
The current sensors can be individual units which are independently wired to the power monitor or individually addressable and daisy chained together to reduce the number of wires required to connect the current sensors to the power monitor. An industrial electrical panel may include eighty or more circuit breakers and a current sensor is required for each branch circuit that is to be monitored. Space is limited in an electrical panel enclosure and the circuit breakers and branch circuit wiring are closely spaced leaving little room for a large number of current sensors and the wiring necessary to connect them to a power monitor.
A plurality of current sensors can be spaced apart on a support that is easily mounted on the panel adjacent to a row of circuit breakers. Preferably, the current sensors are spatially arranged on the support so that the respective apertures in the bodies of the sensors are substantially aligned with the spaced apart connections of the branch circuit wiring to the respective circuit breakers. The sensor outputs can be conducted to the power monitor over a multi-conductor cable substantially reducing the amount of wiring necessary in the panel enclosure. However, if the electrical panel has already been wired, the branch wiring to each of the circuit breakers must be disconnected so that the sensor array can be installed in the panel enclosure and the branch circuit wires can be routed through the central apertures in the current sensors and then reconnected, increasing the time and expense of installing a branch power monitor.
What is desired, therefore, is a sensor for a power monitoring system that can be conveniently installed in a pre-wired panel enclosure.